Delay elements are building blocks of clock distribution networks in some integrated circuits and systems. Delay elements are intended to define a time reference for movement of data within those systems. Variable delay elements are inverter-based circuits used for fine, precise, and accurate pulse delay (or phase) control in high-speed digital integrated circuits. In order to achieve wide delay or phase adjustments, variable delay elements are realized as a chain of inverters. The chain of inverters is called delay line.
In many integrated circuits, delay lines are used in systems such as in DLLs (Delay Locked Loops), TDCs (Time-to-Digital Converters), VCOs (Voltage Controlled Oscillators), Pulse-Width Control Loops (PWCLs), etc. In such applications, variable delay elements are used for precise and accurate pulse time reference.
Double Data Rate circuits, which transfer data on both the rising and falling edges of the clock signal, also use delay lines and delay data or clock delays to achieve appropriate signal timing in a data transmission. Delay lines provide linear steps that are used to tune an input signal delay. However, inconsistent delay step variations increase clock jitters, in some instances.